This is a competitive renewal application for a research grant (Motion Processing System in Schizophrenia R01 MH 61824). In the last grant period (2000-2003), we examined functional properties of representative visual motion processes in schizophrenia. We found that the global, but not the local, stages of the motion system are impaired in schizophrenia, which implicates faulty neural processing in the extrastriate cortex. We found that the motion-processing deficit in schizophrenia is independent of visual contrast modulation, suggesting that the contrast-independent late stage of the motion pathway is affected. Given that the late stages of motion processing in the extrastriate cortex mediate spatial and temporal integration of motion signals, one general hypothesis arising from our findings is that the visual brain system implicated in schizophrenia is unable to function as an ensemble. That is, the whole is not equal to the sum of the parts, in the context of the schizophrenic brain system. The advances of visual neuroscience in the past decades have greatly increased the knowledge about how the different parts of the brain system work together. With the principles developed in visual neurophysiology as a guideline, the proposed studies will focus on how different components of the visual system in schizophrenia are functionally organized, through studying its spatial and temporal structures in individuals with and without schizophrenia. We will determine sensory, motor, and cognitive responses to paired and grouped visual stimuli whose spatial and temporal proximities are systematically varied. We will determine the pattern of visual brain activation in response to motion discrimination events. The outcome of these investigations will indicate how the spatial and temporal interaction across the different processing components of the visual system functions in schizophrenic patients, from which the "whole vs. sum of the parts" hypothesis can be evaluated empirically.